Silicon (Si) is used for a channel of a transistor included in a semiconductor device. In such a configuration in which Si is used, the mobility of carriers cannot be sufficiently increased. Thus, the current flowing through the channel cannot be sufficiently large. As such, the performance of the semiconductor device in which Si is used for the channel is physically limited. To address the above problem, studies were made showing that the performance of the semiconductor device is significantly improved by increasing the current flowing through the channel with a material having a higher carrier mobility than Si, for example, such as indium gallium arsenide (InGaAs), instead of Si.
In order to manufacture a transistor including InGaAs, an InGaAs layer is formed on a semiconductor wafer (hereinafter, referred to as a “wafer”) as a substrate, and subsequently, a high dielectric constant insulating film called a high-k film is laminated by, for example, chemical vapor deposition (CVD). However, there is a case where a natural oxide film is formed on the surface of the InGaAs layer before the formation of the high-k film. If such a natural oxide film is formed at an interface between the high-k film and the InGaAs layer, the interface state density becomes high. This makes it difficult to increase the current of the channel as described above, which degrades the performance of the transistor.
Patent Document 1 describes the removal of arsenic oxide in a resist film using hydrogen fluoride. Patent Document 2 describes that a conductor layer constituting a light emitting diode is made of gallium oxide and the conductor layer may be chemically etched with hydrogen chloride. In this regard, it is considered that the natural oxide film of the InGaAs layer is removed using, for example, a hydrogen chloride gas or a hydrogen fluoride gas as an etching gas. However, in order to remove oxide of indium (In) constituting the natural oxide film of the InGaAs layer using the hydrogen chloride gas or the hydrogen fluoride gas as mentioned above, a compound (InF3) containing indium (In) and fluorine or a compound (GaF3) containing indium (In) and chlorine should be generated and these compounds should be sublimated. In order to generate such compounds, it is necessary to heat the wafer at a relatively high temperature. For example, the generation of InF3 requires heating the wafer at a temperature of 900 degrees C. or higher, and the generation of GaF3 requires heating the wafer at a temperature of 500 degrees C. or higher. At such high temperatures, however, there is a possibility that the wirings of the semiconductor device formed on the wafer may be damaged and the heat resistance limit of a device that performs the removal process of the natural oxide film may be exceeded.
Therefore, it becomes necessary to perform a wet etching process to remove the natural oxide film. In such a wet etching process, the natural oxide film may not be sufficiently removed. Moreover, there is a possibility that the surface of the InGaAs layer may be reoxidized when the wafer processed by the device that performs the wet etching process is carried into a process vessel which is kept in a vacuum atmosphere to form the high-k film.
In addition, Patent Document 3 discloses that indium adhered as a contaminant onto the surface of a substrate used for manufacturing a semiconductor device is removed by supplying oxygen and hexafluoroacetylacetone. However, Patent Document 3 does not describe the removal of a natural oxide film of metal constituting the semiconductor. Therefore, the problem of how to remove the natural oxide film in the semiconductor layer cannot easily be solved by those skilled in the art based on Patent Document 3 mentioned above.